The past decade has seen exciting advances in our understanding of central fear systems, information regarding the extended amygdala, the broader limbic system, their targets and modulating structures, is providing new avenues for the formation of testable models of anxiety disorders that are amongst the most common psychiatric illnesses. Panic disorder (PD) and posttraumatic stress disorder (PTSD) are prime candidates for explication by reference to central fear systems. Further, because they converge and diverge in important ways, PD and PTSD challenge our understanding of how central fear systems can support related yet distinct anxiety syndromes. A strong version of this challenge is presented by the sleep disturbances of PD and PTSD. Both are associated with subjectively disturbed sleep continuity, nocturnal paroxysmal episodes (nocturnal panic attacks and trauma-related nightmares, respectively), and, our data would suggest, suppression of sleep movement. Nevertheless, these two anxiety disorders appear to exhibit divergent modifications of nocturnal respiration, elevated tidal volume variability in PD, versus accelerated respiration in association with nightmares in PTSD. The aim of this project is to lay the foundation for a more comprehensive account of the interaction of sleep and fear systems in PD and PTSD by optimally quantifying domains in which they converge and diverge: arousals from sleep, sleep movements and sleep respiration. In this study, sleep data will be obtained from 180 community-residents, unmedicated, female and male subjects with PD (30 with and 30 without a history of nocturnal panic attacks), PTSD (30 with and 30 without a history of trauma-related nightmares), comorbid PD and PTSD (30), and normal controls. The proposed methods represent an advanced approach to naturalistic sleep data acquisition, combining an initial phase of ambulatory polysomnography (PSG) with extended (21+days) actigraphy and auditory sonography.